Hydraulic spud lifting arrangement for dredges



Sept. 13, 1966 F. J. SCHMIDT HYDRAULIC SPUD LIFTING ARRANGEMENT FOR DREDGES Filed April 16, 1964 2 SheetsSheet 1 INVENTOR.

WWO.

p 3, 1966 F. J. SCHMIDT 3,272,477

HYDRAULIC SPUD LIFTING ARRANGEMENT FOR DREDGES Filed April 16, 1964 2 Sheets-$heet Z United States Patent 3,272,477 HYDRAULIC SPUD LIFTING ARRANGEMENT FOR DRIEDGES Fred J. Schmidt, Baitimore, Md., assignor to Ellicott Machine Corporation, Baltimore, Md, a corporation of Maryland Filed Apr. 16, 1964, Ser. No. 360,333 14 Claims. (Ci. E i-93) This invention relates generally to dredges and more particularly to a dredge including novel and improved hoist means for raising the spud of a dredge and oper able to permit substantially free falling of the spud so the dropping energy of the spud will assist in producing a maximum penetration thereof.

It is common to provide spuds which are mounted on the hull of a floating dredge and are operable to engage the bottom under the body of water to control the posi tion, and sometimes the movement of the dredge hull. Such spuds are connected to the dredge hull by means which permit vertical movement of the spud to permit lifting of the spud clear of the bottom and lowering of the spud into engagement with the bottom. Such spuds are relatively large and heavy so power means are pro vided to control their vertical movement.

The effectiveness of the spud in positively controlling the position or movement of the dredge hull is a function of the amount of penetration of the spud into the bottom. Normally, in the past, the weight of the spud alone has been used to produce this spud penetration. In a dredge incorporating this invention, however, hoist means are provided which are operable to raise the spud and also operable to permit substantially free dropping of the spud so that the velocity of downward movement of the spud assists the dead weight to produce a maximum penetration of the spud into the bottom. The structure for performing this improved function is simple, reliable and economical and is arranged so that the entire hoist can be fabricated as a unit and later installed on the dredge hull.

It is an important object of this invention to provide a novel and improved dredge having a spud and a power mechanism for raising and lowering the spud operable to permit substantially free fall of the spud for maximum penetration thereof.

It is another important object of this invention to provide a dredge having position controlling spuds in combination with hoist means including a piston and cylinder actuator to provide the power for raising the spud and means to allow substantially free fall of the spud.

It is still another object of this invention to provide a novel and improved spud and hoist arrangement for dredges and the like wherein the hoist includes a cable connected to the spud and to a controllable winding drum with the power for raising the spud supplied by a linear actuator engaging the cable intermediate its ends.

It is another important object of this invention to provide a novel and improved spud and hoist combination according to the preceding object wherein a brake is connected to the Winding drum which is operable to lock the drum against rotation and winding means are connected to the winding drum which are operable to rewind the cable onto the drum.

It is still another object of this invention to provide a novel and improved hoist mechanism, according to any of the preceding objects, in combination with a control system therefor which substantially eliminates the need of operator skill and automatically prevents damage to the system.

It is still another object of this invention to provide a novel and improved control system for use with a hoist, according to the last preceding object, wherein operating 3,272,477 Patented Sept. 13, 1966 simplicity and functional versatility is achieved with a minimum expense and equipment.

Further objects and advantages will appear from the following description and drawings, wherein;

FIGURE 1 is a perspective view of a dredge incorporating a spud and spud hoist mechanism incorporating this invention;

FIGURE 2 is an enlarged fragmentary side elevation of the hoist mechanism and spud;

FIGURE 3 is a fragmentary end view of the spud and hoist mechanism with parts broken away for purposes of illustration;

FIGURE 4 is an enlarged fragmentary view of the winding drum, brake and winding motor structure;

FIGURE 5 is a schematic illustration of the brake structure; and

FIGURE 6 is a schematic illustration of the hydraulic control circuit for the hoist mechanism.

This invention is illustrated installed on a conventional hydraulic dredge including a hull and machinery house 11 and dredge ladder 12. Mounted on the stern of the hull 10 are a pair of similar spud. and hoist assemblies 13 and 14. The two assemblies 13 and 14 are similar, therefore, only the assembly 13 will be discussed in detail with the understanding that the discussion applies equally to the assembly 14.

The assembly 13 includes a spud 16 which may be raised clear of the bottom under the water or may be lowered into engagement with the bottom. Thus, the spuds 16 function to provide substantially rigid anchoring of the hull 10 while the dredge is operated. The spuds 16 can be either individually raised or both raised to permit movement of the hull as required during the dredging operation and then again lowered to provide positive anchoring of the dredge.

With a spud and hoist assembly incorporating this invention a maximum amount of penetration of the spud into the bottom can be achieved with a very simple mechanism by merely dropping the spud in substantially free fall so that its inertia assists the weight of the spud in producing penetration of the lower end thereof into the bottom.

Referring now to FIGURES 2 and 3, the spud 16 extends through a pair of spaced guide bearings 17 and 18 mounted on the stern of the hull 10. These bearings permit vertical movement of the spud 16 but prevent lateral or tipping movement. A hoist is mounted on a mast 19 which in the illustrated embodiment is formed of welded tubular struts 21 and 22 connected at their upper end by a bracket 23. Cross struts 24 connect the struts 21 and 22 so that the mast is in the form is of a triangle having spaced mounting plates 26. As is illustrated in FIGURE 3, the mast is formed of parallel triangular frames each consisting of struts 21 and 22. The bracket 23 and cross struts 27 connect the two triangular frames and complete this structure.

The mounting plates 26 are secured by removable pins to brackets 28 welded to the hull deck. This permits the installation or removal of the entire hoist structure as a unit and also permits the separate fabrication of the complete assembly.

To produce the power to raise the spud a hydraulic cylinder 29 is mounted on the cross struts 27 and is provided with a piston 31 which is extendable or retractable relative to the cylinder by fluid under pressure. An upper pulley sheave 32 is provided with three free running pulleys 33 is mounted on the bracket 23 and a lower pulley sheave 34 with two free running pulleys 36 is mounted on the end of the piston 31.

A cable 37 is connected at one end to a collar 38 which fits around the spud 16 and is adjustably locked, to

3 prevent downward movement of the spud relative to the collar, by a cross pin 39 extending through holes in the spud. The spud 16 is provided with a series of spaced holes 41 to receive the cross pin 39 so that the collar may be locked at any one of a number of positions along the spud. Also, a cross pin 42 can be placed in one of the holes 41 and the spud lowered until the cross pin 42 engages the guide bearing 17 to support the spud when it is desired to adjust the collar along the spud or support the spud without placing strain on the hoist.

The cable 37 extends up over one of the pulleys 33 and then down to and around one of the pulleys 36. The cable then extends up again around another one of the pulleys 33 and down around the other pulley 36. From there it extends over the last pulley 33 and down to a winding reel 43 which is mounted on a shaft 44. The shaft 44 is in turn mounted in bearings 46 on either side of the Winding drum 43 which are supported on the mast by a bracket 47.

A brake 48 mounted on one end of the shaft 44 is operable to prevent rotation of the drum 43 or permit rotation thereof and mounted on the other end of the shaft 44 is a hydraulic motor 49 which is operable to rotate the drum 43.

When the brake 48 is applied to prevent rotation of the winding drum 43 and the piston 31 is extended, the spud 16 is lowered. Conversely when the brake 48 remains applied and the piston 31 is retracted the spud 16 is raised. With the illustrated embodiment the distance that the spud 16 is raised or lowered is equal to four times the distance the piston 31 extends or retracts since there are four cable strands extending between the two sheaves 32 and 34. If greater or lesser motion multiplication is required sheaves having different numbers of pulleys and numbers of cable strands may be utilized. In the illustrated embodiment the hydraulic cylinder must be able to provide a retracting force at least equal to four times the weight of the spud 16 with sufficient surplus power to overcome mechanical inefficiencies as well as provide the necessary force to free the spud after it penetrates into the bottom.

When it is desired to drop the spud 16 it is first raised by retracting the cylinder 31. The brake 48 is then released allowing the drum 43 to rotate and permitting cable to feed off the drum. When this is done the weight of the spud 16 carries the spud downward at a rate approaching free fall velocity. If slower dropping rates are desired the brake 48 is only partially released so that it resists the dropping movement of the spud. The brake 48 is arranged so that it can be controlled to produce any desired degree of braking from substantially zero to the maximum or locking braking condition. Therefore, the operator by controlling the brake 48 is able to provide complete control of the rate of the drop of the spud.

In the illustrated embodiment the control circuit is arranged so that the piston 31 commences to extend at the same time the pressure is provided to permit release of the brake 48. The period required for extension of the piston 31, however, is substantially longer than the time required to drop the spud 16, so the piston continues to extend after the spud 16 penetrates into the bottom. The circuit is also arranged so that the motor 49 is pressurized at the same time pressure is applied to permit release of the brake 48. However, the motor 49 has a very small power output when compared to the weight of the spud 16 so it does not appreciably slow the spud in its drop. During the dropping movement of the spud the motor is rotated backwards by the weight of the spud. As soon as the spud 16 comes to rest the motor 49 causes winding rotation of the drum 43 which is permitted by the fact that the brake 48 is released. This causes the slack produced by extension of the piston 31 to be taken up by re winding the cable onto the drum 43. As soon as the piston 31 is in the fully extended position the brake 48 is relocked and the system is again in condition for raising the spud 16.

One form of brake which may be used for the brake 48 is schematically illustrated in FIGURE 5. This is a hand brake having a band 51 which wraps around a drum 52 fixed on the shaft 44. One end of the band 51 is anchored on the frame at 53 and the other end is connected to a lever 54. Lever 54 is pivoted on the frame and is connected at its other end to a piston 56 of a hydraulic cylinder 57. A spring 58 within the cylinder 57 urges the piston 56 to the retracted position and therefore normally applies tension to the band 51 which locks the drum against rotation. When fluid under pressure is supplied to the rearward end of the cylinder 57 through a pressure line 59 the fluid under pressure overcomes the action of the spring 58 and extends the piston 56 to release the brake. The pressure in the cylinder 57 can be controlled from zero to a maximum pressure necessary to produce full release of the brake. Therefore, the operator can control the degree of braking by controlling the pressure in the cylinder.

In FIGURE 6 the hydraulic circuit is illustrated including the controls for each of the hoists of the spud and hoist assemblies 13 and 14. Here again, the detailed description of the control circuit for one hoist applies to the other. A pump 60 receives hydraulic fluid from a reservoir 61 and provides system pressure through lines 62 to the inlet of a four way control valve 63 for each hoist. Each of these valves 63 is of the type which is movable between three positions and arranged so that when in the center position both of the controlled ports are connected to the reservoir returns 64. When the valve 63 is moved to one operated position one of the control ports is connected to the pressure line 62 and the other to the reservoir return 64. Movement of the valves to the other operated position reverses the connections of the control parts thereof. A relief valve 66 connects the pressure line 62 to a reservoir return 67 and limits the maximum supply pressure.

One of the control ports of the valve 63 is connected through a line 69 to the rearward end of the associated cylinder 29, the input of the associated motor 49 and to a fixed flow restriction 68. The out-put of the motor 49 is connected to the return line 67 and the downstream side of the flow restriction 68 is connected through the line '59 to the brake cylinder 57 and to the inlet of a brake control valve 71. The outlet of the valve 71 is connected to the return lines 67. The brake control valves 71 are normally open and are of the type which permit manual closing by operation of a lever 72 coupled so that the valve regulates to produce a pressure in the line 59 determined by the position of the lever 72. Since the pressure line 59 is downstream from the flow restriction 68 the pressure therein approaches the return line pressure when the valve 71 is open and reaches supply pressure when it is closed. Substantially infinite pressures between these two extremes can be produced in the pressure line 59 by appropriate operation of the lever 72. Therefore, the operator may control the brake 48 in any desired manner between full locking and complete release.

The other control port of the valve 63 is connected to the forward end of the associated cylinder 29 through a check valve 73 and a relief valve 74 connected in parallel therewith. The check valve 73 permits substantially unrestricted flow toward the associated cylinder 29 and prevents reverse flow. The relief valve 74 prevents reverse flow when the pressure in the forward end of the associated cylinder 29 is below a predetermined value.

The operation of the control circuit for each of the hoists is as follows. Assuming the spud 16 is in the lower position, the associated piston 31 is extended and the control valve 63 is in the neutral or off position. At this time pressure is not supplied to the circuit and both of the controlled ports are connected to the reservoir. Since the cylinder 29 is not supporting the spud there is no appreciable pressure in the forward end thereof.

When it is desired to raise the spud the control valve 63 is shifted to the left, as viewed in FIGURE 6. This connects the forward end of the associated cylinder 29 to output pressure of the pump 60 through the associated check valve 73. At the same time the rearward end of the associated cylinder 29 and the associated motor 49 and brake cylinder 57 are connected to reservoir return. The spring 58 locks the associated brake while the piston 31 retracts. This causes the sheaves 34 to move away from the sheaves 32 and raises the spud 16. When the spud 16 is raised the desired amount the operator returns the control valve 63 to the neutral position. This can be done at any point in the stroke of the piston 31.

Since the check valve 73 prevents reverse flow and the relief valve 74 remains closed, the piston 31 is hydraulically locked in position and the spud is supported.

When it is desired to lower the spud the control valve 63 is shifted to the right, as viewed in FIGURE 6, to connect the supply pressure to the rearward end of the cylinder 29, to the inlet of the motor 49 and to the flow restriction 68. This produces extension of the piston 31. During such extension there is sufficient pressure developed to open the relief valve 74. The relief valve 73 is set to operate at a pressure which will insure sufficient pressure in the line 59 to operate the brake cylinder 57 even when the weight of the spud is acting on the piston 31. However, the relief pressure of the valve 74 should not be set so that supply pressure cannot extend the piston 31 after the weight of the spud is removed from the hoist such as when the spud is resting on the bottom or when it is supported on the pin 42.

If it is desired to slowly lower the spud the valve 71 is not operated and remains in the open position so the brake 48 remains locked. Such slow lowering of the spud is required when it is desired to lower the pin 42 against the guide bearing 17 and in some instances when the spud is to be lowered into the bottom. The motor 48 although pressurized does not produce sufficient power to cause slipping of the brakes so it merely remains mechanically locked.

If it is desired to drop the spud the operator moves the lever 72 to the desired position to produce the desired rate of dropping after the control valve 63 is shifted to the right, as viewed in FIG. 6. This releases the brake 48 the desired amount and permits the spud to drop at the controlled rate of speed while the piston 31 is extending. During this dropping the motor 49 runs backwards since it does not have sufficient power to significantly affect the rate of dropping. The relief valve 66 protects the motor 49 during such backward rotation by limiting the maximum pressure.

As soon as the spud comes to rest the lever 72 is moved to fully release the brake 4 8 and the motor 49 rotates the drum 43 in the winding direction as the piston 31 continues to extend. This causes the slack to rewind on the drum and continues until the piston 31 reaches its full extended position. The various elements are then again in condition to permit raising of the spud and the control valve 63 is returned to the neutral position. Because the motor 49 is pressurized during the drop it produces a predetermined minimum tension in the cable 37 during the drop. Therefore, backlash cannot occur even if the brake 48 is fully released.

In one embodiment Olf this invention a spud thirty-six feet long having an outside diameter of twelve and threequarters of an inch and weighing 3600 pounds is raised by a six inch hydraulic cylinder 29 having a forty-two inch stroke. Supply pressure is provided by the pump 60 at 1600 pounds per square inch and the relief valve 66 is set to open at 1800 pounds per square inch. The brake 48, when applied, produces 40,000 pound inches and the motor 49 produces 1500 pound inches. This 6 motor torque results in a tension of 325 pounds in the cable.

The motor 49 need only supply sufficient power to prevent damaging backlash and to wind the slack on the winding drum 43, therefore, a very small power output for the motor 49 is all that is needed. In fact, since the motor 49 need not provide any substantial power, it is possible to use other means for slack takeup and backlash prevention is desired. As an example, a mechanical spring reel may be substituted for the motor 49. Such spring reels would resist rotation of the winding drum 43 in the direction permitting the cable to wind off the drum during the drop phase of operation and automatically cause the slack to be rewound onto the drum during the piston extension phase of operation.

Since a prime mover must be provided even on a hoist without the free drop feature, the free drop is achieved with the simple addition of the winding apparatus of FIGURE 4 and the controls therefor. A maximum degree of simplicity is provided and the various component elements of the system are all conventional, therefore, minimum fabrication cost is achieved with a maximum degree of reliability.

Although a preferred embodiment of this invention is illustrated, it is to be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention as defined in the following claims.

What is claimed is:

1. A dredge comprising a hull; a spud mounted for generally vertical movement relative to said hull; a hoist on said hull having a cable operatively connected to said spud to control the vertical position of said spud; said hoist including winding means operatively engaging said cable operable to release cable, take in cable and lock to prevent both release or taking in of cable, said winding means including drive means for automatically applying tension to said cable at all times when it is unlocked to release cable or take in cable; and a linear power actuator operatively connected to said cable operable in one direction to raise said spud when said winding means is locked.

2. A floating apparatus comprising a hull; a spud mounted for generally vertical movement relative to said hall; a hoist on said hull having a cable operatively connected to said spud to control the vertical position of said spud; said hoist including winding means connected to said cable operable to release cable, taken in cable and lock to prevent both release or taking in of cable, said winding means including drive means for automatically applying tension to said cable at all times when it is unlocked to release cable or take up cable, said tension being less than the tension required to support said spud; and a linear power actuator operatively connected to said cable op erable in one direction to raise said spud when said winding means is locked; operation of said winding means to release cable permitting lowering of said spud.

3. A floating apparatus comprising a hull, a spud, guides connecting said spud and hull permitting vertical movement of said spud, 21 hoist on said hull having a cable connected to raise said spud, said hoist including winding means connected to said cable operable to wind in and release cable, brake means connected to lock said winding means and releasable to permit operation thereof, said winding means including drive means for automatically applying tension to said cable whenever said brake means are released, a linear actuator operatively connected to said cable operable upon movement in one direction when said brake means is locked to cause said cable to raise said spud.

4. A dredge comprising a hull, a spud, guides connecting said spud and hull permitting vertical movement of said spud, a hoist on said hull having a cable connected at one end to raise said spud, said hoist including a winding means connected to the other end of said cable operable to wind in and release cable, brake means connected to lock said winding means and releasable to permit operation thereof, said winding means including drive means for automatically applying tension to said cable whenever said brake means are released, a piston and cylinder actuator connected to said cable intermediate its ends operable upon movement in one direction when said brake means is looked to cause said cable to raise said spud, said winding means having insufficient torque to raise said spud.

5. A dredge comprising a hull, a spud, guides connecting said spud and hull permitting vertical movement of said spud, a hoist on said hull having a cable connected at one end to raise said spud, said hoist including a drum connected to the other end of said cable, brake means connected to look said drum and releasable to permit rotation thereof, torque means connected to said drum, said torque means including automatic means operable to apply torque to said drum tending to wind in cable whenever said brake means is released, a piston and cylinder actuator connected to said cable operable upon movement in one direction when said brake means is locked to cause said cable to raise said spud, said torque means having substantially less power than the power required to raise said spud.

6. A floating apparatus comprising a hull, a vertically extending spud mounted for longitudinal movement relative to said hull, a cable hoist connected to raise and lower said spud; said hoist including a linear actuator operable to take up cable to raise said spud and to release cable, a drum connected to said cable operable to wind in and play out cable, a brake operable to resist rotation of said drum, and torque means for said drum, said torque means including automatic means operable to apply a torque tending to rotate said drum in a wind in cable direction whenever said brake is released, said torque having a value substantially lower than the torque required to raise said spud, and controls operable to control the operation of said actuator brake and torque means.

7. A floating apparatus comprising a hull, a vertically extending spud mounted for longitudinal movement relative to said hull, a cable hoist connected to raise and lower said spud; said hoist including a fluid pressure linear actuator operable to take up cable to raise said spud and to release cable, a drum connected to said cable operable to wind in and play out cable, a pressure operated brake operable to resist rotation of said drum, and fluid motor means operable to apply a torque tending to rotate said drum in a wind in cable direction, said torque having a value substantially lower than the torque required to raise said spud, and fluid controls operable to control the operation of said actuator, brake and motor means.

8. A dredge apparatus comprising a hull, a vertically extending spud mounted for longitudinal movement relative to said hull, a cable hoist connected at one end to raise and lower said spud; said hoist including a hydraulic cylinder actuator connected intermediate the ends of said cable operable to take up cable to raise said spud and to release cable, a drum connected to the other end of said cable operable to wind in and play out cable, a hydraulically ope-rated brake operable to resist rotation of said drum, and hydraulic motor means operable to apply a torque tending to rotate said drum in a wind in cable direction, said torque having a value substantially lower than the torque required to raise said spud, release of said brake permitting substantially free falling of said spud, and controls operable to control the operation of said actuator, brake and torque means.

9. A dredge apparatus comprising a hull, a vertically extending spud mounted for longitudinally movement relative to said hull, a cable hoist connected at one end to raise and lower said spud; said hoist including a hydraulic cylinder actuator connected intermediate the ends of said cable operable to take up cable to raise said spud and to release cable, a drum connected to the other end of said cable ope able to wind in and play out cable, a

hydraulically operated brake operable to resist rotation of said drum, and hydraulic motor means operable to apply a torque tending to rotate said drum in *a wind in cable direction, said torque having a value substantially lower than the torque required to raise said spud, release of said brake permitting substantially free falling of said spud, and controls operable to control the operation of said actuator, brake and torque means, said controls being arranged to supply pressure to said motor whenever said brake is released thereby preventing backlash in said cable.

v1t). A floating apparatus comprising a hull, a vertically extending spud mounted for longitudinal movement relative to said hull, a cable hoist connected to raise and lower said spud, said hoist including a hydraulic power actuator operable in one direction to take up cable to raise said spud and operable in the other direction to release cable, a drum connected to said cable operable to wind in and play out cable, a normally locked hydraulically released brake operable to resist rotation of said drum, and hydraulic motor means operable to apply a torque tending to rotate said drum in a wind in cable direction, said torque having a value substantially lower than the torque required to raise said spud, a source of pressure, and controls connected to said source operable to control the operation of said actuator, brake and motor means, said controls including a three position valve, said valve when in one portion supplying pressure to operate said actuator in said one direction while isolating pressure from said motor means and brake, said valve in another position supplying pressure to operate said actuator in said other direction and also supplying pressure to said brake and motor means.

11. A spud hoist comprising a hull, a vertically extending spud mounted on said hull for longitudinal movement relative thereto, a cable hoist operable to raise and lower said spud, and a hydraulic control system for said hoist; said hoist including a double acting cylinder actuator operable in one direction to take up the cable and in the other direction to release cable, a drum connected to said cable, a normally engaged pressure released brake connected to said drum, and a hydraulic motor connected to rotate said drum and wind cable thereon; said control system including a source of pressure, a four way valve operable in one position to supply pressure to said actuator producing actuation in said one direction while isolating both said brake and motor from said source, said valve when in another position supplying pressure to said actuator producing actuation thereof in said other direction and also supplying pressure to said brake and motor, and means retaining back pressure on said actuator when it operates in said other direction.

12. A hoist comprising -a support, a vertically movable member, a cable hoist on said support operable to raise and lower said member, and a hydraulic control system for said hoist; said hoist including a double acting cylinder actuator operable in one direction to take up the cable and in the other direction to release the cable, a drum connected to said cable, a normally engaged pressure released brake connected to said drum, and torque means connected to rotate said drum and wind cable thereon; said control system including a source of pressure, a four way valve operable in one position to supply pressure to said actuator producing actuation in said one direction while isolating said brake from said source, said valve when in another position supplying pressure to said actuator producing actuation thereof in said other direction and also supplying pressure to said brake, means retaining back pressure on said actuator resisting operation in said other direction, said back pressure being sufficiently great to cause said actuator to support said member, and a pressure control operable to control the pres sure at said brake when said valve is in said other posi tion.

13. A dredge comprising a hull, a vertically extending spud mounted on said hull for longitudinal movement relative thereto, a cable hoist operable to raise and lower said spud, and a hydraulic control system for said hoist; said hoist including a double acting cylinder actuator operable in one direction to take up the cable and in the other direction to release the cable, a drum connected to said cable, a normally engaged pressure released brake connected to said drum, and a hydraulic motor connected to rotate said drum and wind cable thereon; said control system including a source of pressure, a four way valve operable in one position to supply pressure to said actuator producing actuation in said one direction while isolating both said brake and motor from said source, said valve when in another position supplying pressure to said actuator producing actuation thereof in said other direction and also supplying pressure to said brake and motor, means retaining back pressure on said actuator resisting operation in said other direction, and a pressure control operable to control the pressure at said brake when said valve is in said other position.

14. A control system for a cable hoist including a double acting hydraulic power actuator, a normally engaged hydraulically released brake, and a hydraulic motor comprising a source of fluid under pressure, a reservoir re turn, a four way valve operable in one position to connect said actuator to said source for actuation in one direction while connecting both said brake and hydraulic motor to the reservoir return, said four way valve while in another position connecting said actuator to said source for actuation in the opposite direction and connecting said source to said motor and brake, back pressure means connected to said actuator maintaining a predetermined back pressure resisting actuator operation in said other direction, and a pressure control system controlling the pressure supplied to said brake when said four way valve is in said other position.

References Cited by the Examiner UNITED STATES PATENTS 1,810,680 6/ 1931 Rothgarn 25493 2,817,447 12/1957 Bianca 254150 X 3,005,273 10/ 1961 Milne 37-64 WILLIAM FELDMAN, Primary Examiner.

OTHELL M. SIMPSON, Examiner. 

1. A DREDGE COMPRISING A HULL; A SPUD MOUNTED FOR GENERALLY VERTICAL MOVEMENT RELATIVE TO SAID HULL; A HOIST ON SAID HULL HAVING A CABLE OPERATIVELY CONNECTED TO SAID SPUD TO CONTROL THE VERTICAL POSITION OF SAID SPUD; SAID HOIST INCLUDING WINDING MEANS OPERATIVELY ENGAGING SAID CABLE OPERABLE TO RELEASE CABLE, TAKE IN CABLE AND LOCK TO PREVENT BOTH RELEASE OR TAKING IN OF CABLE, SAID WINDING MEANS INCLUDING DRIVE MEANS FOR AUTOMATICALLY APPLYING TENSION TO SAID CABLE AT ALL TIMES WHEN IT IS UNLOCKED TO RELEASE CABLE OR TAKE IN CABLE; AND A LINEAR POWER ACTUATOR OPERATIVELY CONNECTED TO SAID CABLE OPERABLE IN ONE DIRECTION TO RAISE SAID SPUD WHEN SAID WINDING MEANS IS LOCKED. 